Tt Systems On New Industrial Units

[danny7299]

Hi all , 

Just wondering , been to a Few units in my time where the commercial unit is a TT system , its fairly new , ... Why would the DNO insist on it being TT ? can we apply for this to be changed ? 

thanks 

Dan 

 

[Blue Duck]

OH supply with nowhere for the protective earthing?

Just randomly stabbing away in the dark!

 

[danny7299]

Narrr there is a transformer is in the industrial park

 

[Lurch]

If they don't provide you with an Earth, they don't have to maintain it, perhaps its a new DNO cost cutting exercise  :innocent

I thought that originally but then it didn't sound right for a commercial site, then even less so if the transformer is adjacent.

Enquiry to the DNO would probably be the best bet, someone muct have made the decision to do it TT.

 

[Andy™]

If they don't provide you with an Earth, they don't have to maintain it, perhaps its a new DNO cost cutting exercise  :innocent

correct, however ESQCR does state that on new connections, an earth is to be provided unless it would be 'inappropriate for reasons of safety'

 

[apprentice87]

Let me guess.. If i am right i will give you a proper explanation later..

Steel framed building... Multi occupancy???

john...

 

[binky]

or sparky couldn't be arsed to take the rods out having previously installed TT systems as temporary supply

 

[Essex1]

Let me guess.. If i am right i will give you a proper explanation later..

Steel framed building... Multi occupancy???

john...

Bang on.

Also the transformer so close could mean the PSC being extremely high. I think.

 

[Essex1]

The highest I have had is 19.9.

 

[danny7299]

hi all thanks for your comments , yeah it is a block of units , steel structure ... come on ... why no PME then ? 

 

[Tony S]

Narrr there is a transformer is in the industrial park

How far away?

 

[apprentice87]

Ok, The DNO WILL NOT supply TNCS to a steel framed multi occupancy structure, end of.

They will supply ONE unit, but all the rest have to have TT

Reason is this;

Say there are 10 customers each with their own TNCS supply. All customers have quite correctly bonded their MET to the frame of the building in their own unit.

Now, at the service head the neutral is connected to the earth, which in turn is connected to the earthing conductor, which is connected to the MET, which is bonded to the shed frame..

Now, electricity will try to take the path of least resistance. So, what happens in practice, is, say the LV main feeding these units is near one end, the service cable to the first supply intake will be comparatively short. So what happens, is that EVERYONES neutral current, will try to flow through bonding conductors and the shed frame, and all try to disappear back down the supply neutral with the least resistance. This is grossly overloaded, and so could burn out and apart from the fire risk, we all know what happens with TNCS when you have a neutral fault...

You can also have problems with all these "stray currents" flowing through the frame of the building causing other effects such as interferance with the proper working of computers and other kit that is liable to be affected by weird magnatic effects caused by the shed now being a live conductor..

john...

 

[Andy™]

of course when supplies were done properly as TNS, this wasnt an issue

 

[Essex1]

I have had a few 'live' pipes from broken earths on TNS systems.

 

[SLIPSHOD & SLAPDASH]

Ok, The DNO WILL NOT supply TNCS to a steel framed multi occupancy structure, end of.

They will supply ONE unit, but all the rest have to have TT

Reason is this;

Say there are 10 customers each with their own TNCS supply. All customers have quite correctly bonded their MET to the frame of the building in their own unit.

Now, at the service head the neutral is connected to the earth, which in turn is connected to the earthing conductor, which is connected to the MET, which is bonded to the shed frame..

Now, electricity will try to take the path of least resistance. So, what happens in practice, is, say the LV main feeding these units is near one end, the service cable to the first supply intake will be comparatively short. So what happens, is that EVERYONES neutral current, will try to flow through bonding conductors and the shed frame, and all try to disappear back down the supply neutral with the least resistance. This is grossly overloaded, and so could burn out and apart from the fire risk, we all know what happens with TNCS when you have a neutral fault...

You can also have problems with all these "stray currents" flowing through the frame of the building causing other effects such as interferance with the proper working of computers and other kit that is liable to be affected by weird magnatic effects caused by the shed now being a live conductor..

john...

Great reply, better than i could have explained. The DNO has also only offered TT to me for new services to existing HMO (brick built) for similar reasons

 

[Tony S]

of course when supplies were done properly as TNS, this wasnt an issue

Im a big TNS fan.......

Unfortunately economics got in the way of common engineering  sense.

Thank god I stuck to industrial. TN-S all the way.

 

[green-hornet]

I love TT at least you have control